Get cracking: pump up the volume

In an ongoing series, cookery writer and Borough Market regular Jenny Chandler explores eggs in all their various forms. This week: sponge, foam and meringue

Words: Jenny ChandlerImage: Paul Thompson

There’s no doubt that eggs are vital in any cake mixture. In a classic Victoria sponge recipe the eggs firm up and set, trapping both the air bubbles that you’ve creamed into the mixture with your whisk and those created by the chemical reactions of the baking powder.

Perhaps more impressively, the egg can go it alone too, without any need of raising agents. When whisked and agitated, proteins in both the whites and yolks begin to unfold and cling to each other, trapping moisture and air in a miraculous foam.

Whole eggs whipped up with sugar form the airy base for the light genoise sponge so beloved by pastry chefs. No baking powder is required, just the air bubbles incorporated into the eggs—it’s not just the gas expanding in the heat that gives the rise, it’s the moisture in the bubbles evaporating and creating yet more gas which in turn expands as well.

Pale, frothy foam You’ll be needing plenty of elbow grease if you’re hoping to achieve the pale, frothy foam by hand with a balloon whisk, but if you have a stand mixer it’s a piece of cake (ahem!). The idea is to achieve a density where a ribbon of mixture will sit on the surface for a few seconds before disappearing back into the foam.

The process is helped with a bit of gentle heat (the mixing bowl is traditionally placed over a pan of hot water) which thickens the egg giving it more strength to trap the air. The advantage of this type of sponge is that it keeps for a few days (as there is little or no fat to stale) and it’s more pliable and resilient, making it the ideal cake for building layers in complex desserts. I love a simple genoise base topped with a creamed mascarpone and marsala mix and a heap of seasonal fresh fruit.

Yolks require a bit of assistance to create a foam. Beaten alone they’ll come to nothing, but add a little liquid and some carefully controlled heat and you can create a fluffy sabayon or zabaglione. These feather-light creations were once restaurant classics, but the lighter foams of molecular gastronomy seem to have swept them aside and it’s been at least a decade since I’ve spotted one on a menu (or prepared one myself for that matter).

The perfect ratio When it comes to lightness, it’s the whites that hold the key. The perfect ratio of liquid to cooperative proteins allows a network of gossamer-light walls to build up, holding together the air and moisture. Over the centuries cooks and chefs have played with the egg white’s incredible ability to lighten a dish. Recipes for ‘snow’ date back to the 1650s, when whites were beaten with straw whisks and sprinkled with sugar and rosewater before cooking.

Cold mousses call upon an added ingredient to help the ‘scaffolding’ of the dish: gelatine or chocolate, which will cool and firm, stopping the delicate foam from eventually collapsing. In hot dishes, whites give you a double whammy: extra volume is created by evaporating moisture and expanding gas in the bubbles and the proteins firm up with the heat to hold the structure together.

Contrary to popular belief, a soufflé can’t fail to rise as long as you’ve folded in some foamy whites—as far as the air bubbles are concerned, the only way is up. Once mastered, soufflés become a quick supper option and an excellent way to use up leftovers.

Meringue is perhaps the pinnacle of whisked egg white perfection and certainly the most indulgent, served with a good dollop of cream. Recipes for floating islands, pavlovas, vacherins and simple meringues are legion, so today I’m sharing a lesser known Spanish recipe for soplillos de Granada where meringue meets chewy nougat-like turrón—a Spanish Christmas speciality.

A few white-whisking facts and tips: A very fresh egg white will be slower to build volume, but it will make a more stable foam that is less likely to ‘weep’ or become grainy.

A cool egg is easier to split but the white will take a little longer to foam.

Egg yolk, fat or oil and any detergents are your absolute enemies when it comes to whisking whites so make sure that your bowl is spotless.

A medium peak, where the tip of the foam droops over like a pixie hat, is ideal for cakes and soufflés while a dryer, firm peak is best for meringues.

A copper bowl helps to create a stable foam where the maximum volume is achieved without the whites becoming crumbly and beginning to collapse. A tiny pinch of cream of tartar added to the whites when you begin beating will have the same result.